Publications and other reference materials referred to herein are numerically referenced in the following text and respectively grouped in the appended Bibliography which immediately precedes the claims.
Currently, in order to achieve high peak and average power pulses having a pulse length of a few ns with good beam quality one should use master oscillator power amplifier (MOPA) fiber systems or solid-state lasers. The reason for this is the fact that in the ns pulse range the limitation on the shortest pulse duration is the time of flight of the photon in the cavity. Accordingly, in order to achieve a 1 ns pulse the cavity should be shorter than 20 cm. Taking into account the fact that this particular cavity should include optical components (such as collimating and focusing optics, polarization optics and q-switch) together with the active medium forces the maximum length of the active fiber to be around 10 cm long. Moreover, it is well known that amplified spontaneous emission (ASE) gain and nearly all non-liner effects are strongly dependent on the length of the light-matter interaction. Accordingly, the shorter the fiber, the lower the ASE gain and induced non-linear effects. However, it is a very serious challenge to design such a system, due to low pump absorption in an active fiber, which diminishes exponentially upon reducing the length of the fiber. Thus the use of short fibers as a gain medium promises to result in highly inefficient laser operation.
It is therefore a purpose of the present invention to provide a laser source based on a very short active fiber (typically tens cm or below) that emits pulses having a pulse duration of a few ns and high peak and average power.
Further purposes and advantages of this invention will appear as the description proceeds.